The present invention relates to a system for optically detecting the presence of an object.
Human vision is the primary sensory agency through which a vehicle is navigated and through which collisions with other vehicles and objects are avoided. Vision is relied on to detect both stationary and moving objects in sufficient time to enable navigational decisions and to permit effective evasive action. To aid visual detection, many vehicles, structures and other objects are painted, marked or equipped with lighting systems intended to increase the conspicuousness of the object and the likelihood that the object will be observed.
Vehicles, including aircraft, emergency vehicles and slow moving vehicles; structures, such as tall buildings, communication towers and power lines; and other objects, such as runways and highway and other hazard warning signage, are commonly equipped with lighting systems that are intended to draw the attention of potential observers. These lighting systems typically comprise variable intensity or flashing lights which are commonly accepted to be superior to steady-state illumination for attracting human attention. For example, Federal Aviation Administration (FAA) regulations require that aircraft be equipped with an anti-collision lighting system comprising sufficient numbers of flashing lights arranged to illuminate the vital areas around the airplane, considering its physical configuration and flight characteristics, and covering a field extending 75 degrees above and below the horizontal plane of the aircraft. In addition to the anti-collision lighting system, aircraft are equipped with external recognition lights, including a position light system comprising red and green forward lights to distinguish the right and left sides of the plane and a rear mounted white light. Similarly, emergency vehicles and slow moving vehicles are commonly equipped with one or more flashing lights intended to make the vehicle more conspicuous to potential observers, including operators of other vehicles.
However, psychological factors, such as inattentiveness and fatigue; physiological limitations of human vision; atmospheric conditions and visual obstructions commonly prevent observation of objects of interest, including objects that might threaten collision or be important to navigation even if they are equipped with attention attracting lights. For example, more than 80% of mid-air collisions involve a first aircraft overtaking a second aircraft at a converging angle. Any one of many factors, including psychological and physiological factors, may explain the failure of a pilot of an overtaking aircraft to observe flashing lights of the anti-collision system of an aircraft being overtaken. On the other hand, even if the pilot's attention were focused to the rear, in all likelihood, the structure of the aircraft that is being overtaken would block the pilot's view of the overtaking aircraft.
Campanella, U.S. Pat. No. 3,652,981, discloses a proximity warning system based on the detection of the illumination of an exterior flash lamp or strobe mounted on a first aircraft by one or more electro-optical sensors in a second aircraft. The output of the electro-optical sensor is displayed in the cockpit to warn of nearby traffic and an audible alarm may emit an aural tone to draw the pilot's attention to the display. The system detects the presence of one or more sources of light emissions and provides an indication of the relative positions of the detected light source and the detector. However, generally, the system does not distinguish between light sources. Many objects of interest, such as airplanes, include multiple light sources. Including combinations of steady-state and flashing lights, and the environment, such as the vicinity of an urban airport or a crowded highway, may include large numbers of sources of light emissions, only a few of which may be of interest. Distinguishing between sources of illumination aids in rapid identification of sources of interest and enables more timely decision making concerning the significance of the source to the potential human observer. Campanella does disclose an embodiment of the proximity warning system in which a weather radar of one airplane is used to initiate flashing of a light in a second plane. The appearance of a new source of light may aid in distinguishing the flashing light associated with the second airplane from other light emitters in the vicinity. However, weather radar is typically only focused forward and many vehicles, including many aircraft, are not equipped with radar.
What is desired, therefore, is an optically-based system for detecting the presence of objects that are likely to be of interest to a human observer.